1. Field of the Invention
The present invention relates to a semiconductor device. More particularly, the present invention relates to a semiconductor device having a passivation film formed on a semiconductor substrate layer in which circuit elements are provided.
2. Description of the Related Art
IC chips are well known in which a large number of circuit elements such as transistors, aluminum wirings and pads are provided on one semiconductor substrate. FIG. 11 is a cross-sectional view showing a portion of a related IC chip. An insulating film 4 is formed on an element formation layer 2 on which transistors (not shown) and other elements are provided. On a surface of IC chip, a a passivation film 14 is formed.
By forming the passivation film 14, it is possible to physically protect the transistors and aluminum wirings 6, 8, and it is also possible to prevent water from infiltrating IC chips.
However, the above conventional IC chip has the following disadvantages. When transistors arranged in IC chip is operated, the transistors generate heat. A portion of the thus generated heat is emitted outside through the passivation film 14. However, an upper surface of the passivation film 14 is almost flat except for portions in the peripheries of the aluminum wirings 6, 8 and pads 10, 12.
Therefore, the heat radiation efficiency is not sufficient because heat is emitted through the passivation film 14. Accordingly, an increased temperature of the chip causes limitations for further enhancement of the transistor performance. The above problem is very serious especially in IC chips, which generate a large amount of heat, such as IC chips having power transistors or CPU. Also, the above problem is very serious especially in IC chips, having a passivation film formed on a base layer of the insulating film 4, planalized by the method of CMP (chemical and mechanical polishing) for the purpose of high integration.
It is therefore an object of the present invention to solve the above problems and provide a semiconductor device having a passivation film (protective film), the heat radiation efficiency of which is improved.
In the first aspect of the semiconductor device of the present invention, at least part of the passivation film being uneven shaped film, an upper surface of which is formed into an uneven shape independent of a shape of a lower surface of the passivation film layer.
Accordingly, even in the case that a base layer on which the passivation film is formed is flat, it is possible to form an upper surface of the passivation film into an uneven surface. For the above reasons, it is possible to increase a surface area of the passivation film per unit projected area. Consequently, a heat radiating area of the passivation film can be increased. As a result, a larger amount of heat can be emitted outside through the passivation film. In other words, it is possible to enhance the heat radiation efficiency through the passivation film. As a result, it is possible to enhance the performance of the semiconductor device.
In the second aspect of the semiconductor device, the passivation film is formed so as to include thick portions having large thickness of the film and thin portions having small thickness of the film, in an area in which the circuit element is formed.
In the third aspect of the semiconductor device, the passivation film is formed on a planarized insulating layer as a base layer.
In the fourth aspect of the semiconductor device, the base layer is planarized by the CMP method.
In the fifth aspect of the semiconductor device, the base layer includes an insulating layer planarized by the CMP method and a wiring section formed on a part of the insulating layer.
Recently, planarization of the surface of the semiconductor device is regarded as important in view of micronization and high-integration of the semiconductor device.
According to the above configuration, even in the semiconductor device in which the base layer is planarized, the heat radiation area can be increased and thereby the efficiency of the heat radiation through the passivation film can be enhanced. Further, as the film thickness is varied in accordance with a state of circuit elements formed in the base layer, so as to have large thickness at that portions such thickness is required and so as to have small thickness at any portions other than the portions at which the large thickness is required, the heat radiation efficiency can be enhanced while keeping reliability thereof.
In the sixth aspect of the semiconductor device, wherein at least one of the thin portions and the thick portions are arranged so as to be a closest packing structure.
In the seventh aspect of the semiconductor device, the thin or thick portions are regularly arranged such that the each center of adjacent thin or thick portions form a regular triangle.
Accordingly, the surface area of the uneven passivation film can be made maximum within a range of restriction of processing technique. Accordingly, it is possible to further enhance the heat radiation efficiency through the passivation film.
In the eighth aspect of the semiconductor device, the thin portion is formed so as to be the minimum thickness capable of protecting the circuit element.
Accordingly, even if the surface area is the same, it is possible to obtain the passivation film, the average film thickness of which is thinner. Therefore, it is possible to further enhance the heat radiation efficiency through the passivation film.
In the ninth aspect of the semiconductor device, the uneven shaped area may be formed into a shape such that a plurality of independent thick portions are provided on the passivation film which is substantially planar.
Accordingly, as compared with a case that a plurality of independent thin portions are provided on an upper surface of a flat passivation film, even if the surface area, the film thickness of the thin portion and the film thickness of the thick portion are respectively the same, it is possible to obtain an uneven passivation film, the average film thickness of which is thinner. Therefore, it is possible to further enhance the heat radiation efficiency through the the passivation film.
In the tenth aspect of the semiconductor device, at least one of corner portions of the each thin portion and each thick portion defined by the each thin portion may be rounded.
When the corner portions of the each thin portion is rounded, stress concentration caused in the corners of the thin portion can be reduced. Therefore, even if the passivation film is deformed, it is possible to reduce a possibility that the thin portion of the uneven passivation film is broken.
When the corners of the each thick portion are tapered, even if an upper surface of the semiconductor device is covered with a sealing material, stress concentration caused in the sealing material at a position opposed to the corner of the thick portion can be reduced. Therefore, even if the sealing material is deformed, it is possible to reduce a possibility that the sealing material is broken. As a result, it is possible to reduce a possibility that the semiconductor device itself is broken.
That is, while a function of protecting the circuit elements are protected physically, the heat radiation efficiency through the passivation film can be enhanced.
In the eleventh aspect of the semiconductor device, the uneven shaped film is formed in a vicinity of the circuit element generates a large amount of heat generation, the vicinity includes at least a part of above the circuit element.
Therefore, it is possible to emit heat generated by the circuit elements more effectively. Accordingly, while a portion in which the uneven passivation film is formed is minimized, the heat radiation efficiency through the passivation film can be enhanced, which is effective when it is necessary to reduce a portion in which the uneven surface film is formed.
In the twelfth aspect of the semiconductor device, a base layer on which the passivation film is to be formed includes insulating film covers the circuit element, and a plurality of conductive sections formed on a part of the insulating film, and the uneven shaped film is arranged between the conductive sections.
Accordingly, in a portion which is located between the conductive sections, in which no circuit elements such as other conductive sections exist immediately below the passivation film, no problems are caused even if the thickness of the passivation film is reduced. Due to the foregoing, it is possible to form an uneven passivation film, the thin portion of which is thin. That is, it becomes possible to form an uneven passivation film, the average film thickness of which is small and the heat radiation efficiency of which is high.
In the thirteenth aspect of the semiconductor device, an electric potential difference may exist between the conductive sections.
Therefore, it is possible to increase an electric resistance of the passivation film which corresponds to a path of leak current flowing between the conductive sections having an electric potential difference. Therefore, the insulating property between the conductive sections can be enhanced. In the case where a passivation film having a very low electric conductivity is used for the purpose of releasing an electric charge accumulated on and in the passivation film, there is a tendency that the insulating property between the conductive sections is lowered. In this case, it is possible to enhance the insulating property between the conductive sections by providing an uneven passivation film between the conductive sections, which is very preferable.
In the fourteenth aspect of the semiconductor device, the conductive sections may include conductive sections exposed from the passivation film, and the uneven shaped film is arranged between the exposed conductive sections having the electric potential difference therebetween.
Accordingly, it is possible to extend length of the conductive path on the passivation film surface on which a leak electric current flows most easily among the paths of leak currents flowing between the exposed conductive sections.
In the fifteenth aspect of the semiconductor device, the semiconductor device may further comprise a base layer on which the passivation film is to be formed includes insulating film, and at least two wiring sections formed on a part of the insulating film, and the uneven shaped film has at least one groove portion of the thin portion extending in parallel with at least one of the wiring sections.
Accordingly, the electric resistance of the passivation film, which is a path of leak current, can be enlarged and thereby insulating property between the wiring section can be enhanced.
In the sixteenth aspect of the semiconductor device, the semiconductor device may further comprise at least two electrode pads exposed from the passivation film,and the uneven shaped film has an uneven surface between the electrode pads.
Due to the electric potential difference between the electrode pads, the leak current tends to flow therebetween. According to the above configuration, since the uneven area is arranged between the pads, the current path is elongated and thereby the electric resistance therebetween can be increased. Accordingly, such the leak current can be reduced.
In the seventeenth aspect of the semiconductor device, passivation film may include at least one of silicon-rich SiN film, silicon-rich SiO film and silicon-rich SiON film.
In case such materials having a little conductivity such as silicon-rich SiN film, silicon-rich SiO film and silicon-rich SiON film are adopted as the passivation film, it is so effective to reduce the leak current.
In the eighteenth aspect of the semiconductor device, the passivation film may include a first insulating layer and a second insulating layer covered on the first insulating layer and having etching selectivity with respect to the first insulating layer, and portions where the second insulating layer is selectively removed and thereby only the first insulating layer remains constitute the thin portions.
Accordingly, degree of the etching can be controlled with high accuracy. Further, since the thin portion is constituted by the lower film and the thick portion is constituted by the two-layer film, there can be obtained a passivation film with high heat radiation efficiency and high reliability.
In the nineteenth aspect of the semiconductor device, passivation film may include first silicon oxide film, silicon nitride film laminated on the first silicon oxide film and second silicon oxide film laminated on the silicon nitride film, the thin portions are constituted by the first silicon oxide film and the silicon nitride film, and the thick portions are constituted by the first silicon oxide film, the silicon nitride film and the second silicon oxide film.
Accordingly, even in the thin portions, two-layer film can be obtained. Therefore, the passivation effect thereof can be enhanced.
In the twentieth aspect of the semiconductor device, the passivation film is formed so as to include thick portions having large thickness of the film and thin portions having small thickness of the film, on an area in which the circuit element is formed.
According to the above configuration, even if the surface of the element formation area is planar, since the passivation film includes therein the thin and thick portions, the heat radiation efficiency can be enhanced while keeping the flatness of the film surface.
Here, the passivation film is defined as a film having a surface with high reliability with respect to the initial characteristics and the variation with time by suppressing unstableness of the surface thereof. It represents the chemical surface treating, the protective film forming, processing for surface shape, or the combination thereof.